The present invention relates to intravascular stent implants for maintaining vascular patency in humans and animals. More particularly, the present invention provides a radially-expandable stent with a controllable force profile and methods of deploying the stent.
Percutaneous transluminal coronary angioplasty (PTCA) is used to increase the lumen diameter of a coronary artery partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. Typically a first guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the first guidewire to a point just proximal of the stenosis. The first guidewire is then removed. A balloon catheter on a smaller 0.014 inch diameter second guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The second guidewire is advanced into the stenosis, followed by the balloon on the distal end of the catheter. The balloon is inflated causing the site of the stenosis to widen.
The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. It has also been shown that the use of intravascular stents can measurably decrease the incidence of restenosis after angioplasty thereby reducing the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel reclosure. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in diameter from small coronary vessels of 3 mm or less to 28 mm in the aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A typical stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A typical stent ranges from 5 mm to 50 mm in length. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. The stent expands radially as the balloon is inflated, forcing the stent into contact with the interior of the body lumen thereby forming a supporting relationship with the vessel walls.
Conventional angioplasty balloons fall into high, medium and low pressure ranges. Low pressure balloons are those which fall into rated burst pressures below 6 atmospheres. Medium pressure balloons are those which fall into rated burst pressures between 6 and 12 atmospheres. High pressure balloons are those which fall into rated burst pressures above 12 atmospheres. Burst pressure is determined by material selection, wall thickness and tensile strength.
The biocompatible metal stent props open blocked coronary arteries, keeping them from reclosing after balloon angioplasty. A balloon of appropriate size and pressure is first used to open the lesion. The process is repeated with a stent crimped on a second balloon. The second balloon may be a high pressure type of balloon, e.g., more than 12 atmospheres, to insure that the stent is fully deployed upon inflation. The stent is deployed when the balloon is inflated. The stent remains as a permanent scaffold after the balloon is withdrawn. A high pressure balloon is preferable for stent deployment because the stent must be forced against the artery""s interior wall so that it will fully expand thereby precluding the ends of the stent from hanging down into the channel encouraging the formation of thrombus.
Various shapes of stents are known in the art. U.S. Pat. No. 4,649,922 (Wiktor) discloses a linearly expandable spring-like stent. U.S. Pat. No. 4,886,062 (Wiktor) discloses a two-dimensional zigzag form, typically a sinusoidal form. U.S. Pat. No. 4,969,458 (Wiktor) discloses a stent wire coiled into a limited number of turns wound in one direction, then reversed and wound in the opposite direction with the same number of turns, then reversed again and so on until a desired length is obtained.
Stents have limited ability to provide effective patching of perforated vessels due to the spacing between metal elements. U.S. Pat. No. 4,878,906 (Lindeman et al.) describes an endoprosthesis made of a thin wall molded plastic sleeve intended to be collapsed radially and delivered to a damaged area of a vessel where it is expanded to provide a sealed interface to the vessel on its outer peripheral ends. The endoprosthesis therefore provides a patch which prevents leakage of blood from a vessel wall. The endoprosthesis disclosed employs various molded-in ribs, struts and the like to adapt the device for particular applications and to provide the desired degree of stiffness to form the sealed interface with the vessel wall. Such a stiff prosthesis, however, could not be expected to have the longitudinal flexibility needed to adapt to curved vessels.
One problem with self-expanding stents is that the stents must be compressed into a small diameter for delivery to the site or portion of the body lumen at which support is desired. It is preferable that the stents be compressed into as small of a diameter as possible (typically referred to as xe2x80x9cprofilexe2x80x9d) to assist in delivering the stent to the desired site. That compression can, in some cases cause localized areas of high bending stress/strain within the stent.
As a result of the high bending stresses/strain, the minimum profile for the self-expanding stents can be limited to prevent non-recoverable strain levels in the stent and, therefore, ensure full radial expansion of the stent when released from the delivery system. The larger profile can limit the delivery and use of the stent to larger diameter lumens.
Alternatively, if a small delivery profile is desired, then the stent may be designed to achieve that profile which can often result in a larger window area and a reduction in the outward forces generated by the stent after expansion within the lumen. The larger window area and, therefore, inferior body lumen scaffolding reduces the effectiveness against recurring restenosis. The reduced outward forces may be problematic if the stent does not firmly engage the wall of the lumen.
One attempt at addressing the high bending stresses/strains in a self-expanding stent is described in U.S. Pat. No. 4,830,003 (Wolff et al.) in which the stent is made of a series of generally straight wire segments welded together at their ends to form a zigzag shaped stent when expanded. By using generally straight wires, the bending stresses/strains associated with bends in an integral wire-formed stent body can be avoided. Disadvantages associated with this approach include, however, the cost of manufacturing the stents by welding. The welds also lower the allowable stress levels in the stent, thereby limiting its fatigue life and compression for delivery. Another disadvantage is that the length of the stent can change significantly from the compressed state to the expanded state, thereby making accurate placement of the stent at the desired location within a body lumen more difficult.
Another attempt at addressing the high bending stresses/strains includes manufacturing self-expanding stents from materials other than metals as described in, e.g., U.S. Pat. No. 5,356,423 (Tihon et al.). The stents disclosed therein are formed of thermoplastic materials and can be molded or otherwise formed into a fenestrated pattern similar to those produced by braided wire stents. By shaping the openings as depicted in FIG. 5 of the patent, the stress concentration at the bending points can be reduced. Disadvantages of this approach include, however, degradation associated with implanted plastic materials, including changes in the elasticity of the plastics which can result in a reduction in the radially outward forces generated by the stent.
Another problem associated with self-expanding stents is that, particularly in connection with long lesions (e.g., those with a length of about 30 mm or more), differences in vessel diameter between the proximal and distal ends of the lesion and/or stent may be greater than the desired operating range of a self-expanding stent. Furthermore, the increase in over-sizing from the proximal to the distal end of the stent may result in non-uniform pressure at the vessel wall along the length of the stent. That non-uniformity may cause insufficient or excessive pressure at one end of the stent after expansion.
Yet another problem with self-expanding stents is the need for stents that can provided varying outward force or pressure along their lengths. Attempts to provide stents with varying outward pressure profiles are typically limited to helically wound stents in which the coil density and/or helix angle are changed to affect the pressure generated by the stents after expansion. See, e.g., U.S. Pat. No. 5,246,445 (Yachia et al.) and U.S. Pat. No. 5,507,767 (Maeda et al.). These approaches are generally limited to gradual pressure changes and may be difficult to construct. In addition, changing the pitch of the helically wound stents can increase the size of the openings between adjacent windings, thereby reducing support of the vessel wall.
Another approach to providing a stent with a varying pressure profile is described in U.S. Pat. No. 5,601,593 (Freitag) in which rows of Nitinol wires with different shape memories that allow for selective expansion of the different structures formed by the different wires. One problem with this approach is that the pressure generated between the activated wires can be significantly reduced, thereby reducing uniformity in the outward force along the entire length of the stent.
It is an object of the invention to provide a self-expanding stent for implantation within a body lumen that provides for controllable expansive force profile when delivered to a desired location within a body lumen.
It is another object of the invention to provide a self-expanding stent with a conical shape having an increasing expanded diameter along the length of the stent.
It is a further object of the invention to provide a stent with improved longitudinal flexibility to allow for threading through tortuous lumens and lesions, as well as to permit implantation in highly curved lumens.
In one aspect, the present invention provides a radially expandable stent for implantation within a body lumen including an elongated generally tubular body defining a passageway having a longitudinal axis. The body includes a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a longitudinal length along the longitudinal axis. Each of the circumferential support sections includes a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section. The stent further includes at least one longitudinal member connecting adjacent support sections in the body. Each of the circumferential support sections is radially compressible into a compressed diameter and radially expandable into an unrestrained expanded diameter in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern. In addition, the longitudinal lengths of at least two of the circumferential support sections are different.
In another aspect the present invention provides a radially expandable stent for implantation within a body lumen including an elongated generally tubular body defining a passageway having a longitudinal axis. The body includes a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a longitudinal length along the longitudinal axis.
Each of the circumferential support sections includes a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section. The stent further includes at least one longitudinal member connecting adjacent support sections in the body. Each of the circumferential support sections is radially compressible into a compressed diameter and radially expandable into an unrestrained expanded diameter in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern, and further wherein the unrestrained expanded diameters of at least two of the support sections vary.
In another aspect, the present invention provides a radially expandable stent for implantation within a body lumen including an elongated generally tubular body defining a passageway having a longitudinal axis. The body includes a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a longitudinal length along the longitudinal axis. Each of the circumferential support sections includes a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section. The stent further includes at least one longitudinal member connecting adjacent support sections in the body. Each of the circumferential support sections is radially compressible into a compressed diameter and radially expandable into an unrestrained expanded diameter in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern. In addition, the circumferential width of the struts in at least two of the circumferential support sections are different.
In another aspect, the present invention provides a method of deploying a stent within a body lumen by providing a radially expandable stent including an elongated generally tubular body defining a passageway having a longitudinal axis. The body includes a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a longitudinal length along the longitudinal axis. Each of the circumferential support sections includes a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section. The stent further includes at least one longitudinal member connecting adjacent support sections in the body. Each of the circumferential support sections is radially compressible into the compressed diameter and radially expandable into an unrestrained expanded diameter in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern. In addition, the longitudinal lengths of at least two of the circumferential support sections are different. The method further includes advancing the distal end of the delivery device and the stent through a body lumen and deploying the stent at a desired location within the body lumen.
In another aspect, the present invention provides a method of deploying a stent within a body lumen by providing a radially expandable stent including an elongated generally tubular body defining a passageway having a longitudinal axis. The body includes a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a longitudinal length along the longitudinal axis. Each of the circumferential support sections includes a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section. The stent further includes at least one longitudinal member connecting adjacent support sections in the body. Each of the circumferential support sections is radially compressible into the compressed diameter and radially expandable into an unrestrained expanded diameter in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern, and further wherein the unrestrained expanded diameters of at least two of the support sections vary. The method further includes advancing the distal end of the delivery device and the stent through a body lumen and deploying the stent at a desired location within the body lumen.
In another aspect, the present invention provides a method of deploying a stent within a body lumen by providing a radially expandable stent including an elongated generally tubular body defining a passageway having a longitudinal axis. The body includes a plurality of circumferential support sections arranged successively along the longitudinal axis, each of the support sections having a longitudinal length along the longitudinal axis. Each of the circumferential support sections includes a plurality of primary bends interconnected by struts, the primary bends being located on alternating ends of the support section around the circumference of the body, each of the struts connecting successive primary bends on opposite ends of the support section. The stent further includes at least one longitudinal member connecting adjacent support sections in the body. Each of the circumferential support sections is radially compressible into the compressed diameter and radially expandable into an unrestrained expanded diameter in which the struts and the primary bends in each of the support sections are arranged in a zigzag pattern. In addition, the circumferential widths of the struts in at least two of the circumferential support sections are different. The method further includes advancing the distal end of the delivery device and the stent through a body lumen and deploying the stent at a desired location within the body lumen.
These and other features and advantages of the present invention are described below in connection the description of the preferred embodiments.